Phosphorus Relationships in Runoff from Fertilized Soils

The effect of P fertilizer mixed into soil on the P composition of runoff was studied. Runoff samples from artificial rainstorms on fallow plots of Russell sil soil, and P enriched soil‐water mixtures (1:50) of Russell sil and selected other soils were analyzed for water soluble orthophosphate and extractable, total, and organic P in sediment. The relation of P addition rate to the soluble orthophosphate or sediment extractable phosphorus level in runoff was approximately linear. The relation of soluble orthophosphate to extractable P in soil‐water systems was linear for most soils studied. Soluble orthophosphate and extractable P in sediment were not related to total P or to organic P in sediment. A procedure was suggested for estimating the soluble orthophosphate concentration in runoff from fertilized wet soil using laboratory analyses.